As the overall dimensions of semiconductor devices continue to shrink, the demand is ever increasing for devices having large charge storage capacity. The need for large charge storage capacity remains even though individual components are scaled to smaller dimensions. As the surface area of a component, such as a capacitor is reduced, a corresponding reduction in charge storage capability occurs. The smaller surface area available for components, such as transistors, capacitors, and the like, coupled with the requirement to maintain high charge storage levels has led researchers in the field of fabrication science to seek new materials from which to construct the components. The use of ferroelectric materials eliminates the need for the large surface-area capacitors typically used to store a static electric charge. One group of promising new ferroelectric materials is the family of PZT ceramic dielectrics. The PZT dielectrics have ferroelectric compounds including lead (Pb), zirconium (Zr), and titanium (Ti) oxides; hence the acronym "PZT."
While ferroelectric materials offer a means to obtain high charge storage density, PZT materials possess characteristics that make the integration of a ferroelectric capacitor into a semiconductor device difficult. For example, in the construction of a ferroelectric capacitor using a PZT material, an electrode material is selected, so that it does not chemically react with the PZT material during processing. An unwanted chemical reaction between an electrode material and the PZT can destroy the ferroelectrical properties of the ferroelectric capacitor. The requirement of non-reactivity limits the selection of materials that can be used to form the electrode plates of a ferroelectric capacitor. One suitable electrode material is platinum. Platinum possesses the desired degree of electrical conductivity and does not significantly react with ferroelectric materials, such as PZT. However, platinum is difficult to etch. An ion milling process may be used to define high resolution features from a blanket platinum layer. An etching mask is defined on the platinum surface and an energetic stream of ions bombards the exposed platinum surface. While ion milling can be used to from patterns in a platinum layer, the ion milling process is typically not selective to many masking materials and to layers underlying the platinum layer. The ion milling process removes most materials at about the same rate making control of the process difficult.
The successful fabrication of a ferroelectric capacitor also requires high-resolution patterning capability of the PZT layer. Ion milling processes are unable to etch PZT with sufficient selectivity to other materials. A wet etching process is disclosed in U.S. Pat. No. 4,759,823 to D. Asselanis, et al. The etch includes a two-step process, wherein the first step etches a PZT layer and the second step removes lead residue from the substrate surface once the PZT is removed. Although this method is effective in removing PZT, the etch rate of the first etch step is high and endpoint determination is difficult. In addition, the second step is inefficient and can result in leaching lead from the PZT material underlying the photoresist layer.